<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>属性选择器</title>
</head>
<script src="../js/jquery-3.3.1.min.js"></script>
<body>
<select id="select">
    <option value="">北京</option>
    <option value="">上海</option>

</select>
<button onclick="add()">添加一个城市</button>

</body>
<script>
    let html = $("#select").html();
    html+='<option value="">深圳</option>';
    $("#select").html(html);
</script>
</html>